Namkung, Ju. Phonological Inventories of Tibeto-Burman Languages. 1996. hh:hld:Namkung:Tibeto-Burman
Not sure about allophones of stops before /i/.
The glottal stop only appears syllable-finally, and is "just one phonetic aspect of a phonemic feature that includes pitch." High tone follows syllables ending in glottal stop, and low tone follows syllables without glottal stop.
Diphthongs can't combine with any finals but the glottal stop, so they're probably Vj Vw sequences.